Intermolecular Vibrations in Hydrophobic Amino Acid Crystals: Experiments and Calculations

Intermolecular vibrations of amino acid crystals occur in the THz, or far-infrared, region of the electromagnetic spectrum. We have measured the THz and Raman spectra of dl-leucine as well as two polymorphs of dl-valine, the spectroscopic properties of which have not previously been compared. Theore...

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Bibliographic Details
Published in:The journal of physical chemistry. B 2013-09, Vol.117 (36), p.10444-10461
Main Authors: Williams, Michael R. C, Aschaffenburg, Daniel J, Ofori-Okai, Benjamin K, Schmuttenmaer, Charles A
Format: Article
Language:English
Subjects:
Amino acids
Biological and medical sciences
Correlation
Crystallization
Crystals
Density functional theory
Fundamental and applied biological sciences. Psychology
Hydrogen Bonding
Hydrophobic and Hydrophilic Interactions
Leucine - chemistry
Mathematical models
Molecular biophysics
Physical chemistry
Physico-chemical properties of biomolecules
Spectrum Analysis, Raman
Static Electricity
Stereoisomerism
Valine - chemistry
Vibration
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Summary:Intermolecular vibrations of amino acid crystals occur in the THz, or far-infrared, region of the electromagnetic spectrum. We have measured the THz and Raman spectra of dl-leucine as well as two polymorphs of dl-valine, the spectroscopic properties of which have not previously been compared. Theoretical modeling of intermolecular vibrations in hydrophobic amino acids is challenging because the van der Waals interactions between molecules are not accounted for in standard density functional theory. Therefore, to calculate the vibrational modes, we used a recently developed approach that includes these nonlocal electron correlation forces. We discuss methods for comparing results from different theoretical models using metrics other than calculated vibrational frequency and intensity, and we also report a new approach enabling concise comparison of vibrational modes that involve complicated mixtures of inter- and intramolecular displacements.
ISSN:1520-6106
1520-5207
DOI:10.1021/jp406730a